How do I export a package symbol to a namespace in Perl?

Question

I'm having trouble understanding how to export a package symbol to a namespace. I've followed the documentation almost identically, but it seems to not know about any of the exporting symbols.

mod.pm

#!/usr/bin/perl

package mod;

use strict;
use warnings;

require Exporter;

@ISA = qw(Exporter);
@EXPORT=qw($a);


our $a=(1);

1;

test.pl

$ cat test.pl
#!/usr/bin/perl

use mod;

print($a);

This is the result of running it

$ ./test.pl
Global symbol "@ISA" requires explicit package name at mod.pm line 10.
Global symbol "@EXPORT" requires explicit package name at mod.pm line 11.
Compilation failed in require at ./test.pl line 3.
BEGIN failed--compilation aborted at ./test.pl line 3.

$ perl -version
This is perl, v5.8.4 built for sun4-solaris-64int

Answer 1

Try this:

package mod;                # Package name same as module.

use strict;
use warnings;

use base qw(Exporter);

our @ISA    = qw(Exporter); # Use our.
our @EXPORT = qw($z);       # Use our. Also $a is a bad variable name
                            # because of its special role for sort().

our $z = 1;

1;

Answer 2

It's not telling you that you're having a problem exporting $a. It's telling you that you're having a problem declaring @ISA and @EXPORT. @ISA and @EXPORT are package variables and under strict, they need to be declared with the our keyword (or imported from other modules--but that is not likely with those two). They are semantically different--but not functionally different--from $a.

Nanny NOTE: @EXPORT is not considered polite. Through Exporter it dumps its symbols in the using package. Chances are if you think something is good to export--and it is--then it will be worth it for the user to request it. Use @EXPORT_OK instead.

Answer 3

Others have correctly identified the problem and offered solutions. I thought it would be useful to point out a debugging tip. To isolate a problem to a given file, you can attempt to compile just that file using perl -c(refer to perlrun):

perl -c mod.pm

This would have given you the same error message, leading you to realize the problem is in your .pm file, not your .pl file.